resolved broken pipe issue (#885)

components/device-mgt/org.wso2.carbon.device.mgt.ui/src/main/resources/jaggeryapps/devicemgt/app/units/cdmf.unit.default.device.type.realtime.analytics-view/public/js/device-stats.js

@@ -25,9 +25,9 @@ $(window).load(function () {
     connect(websocketUrl)
 });
 
-$(window).unload(function () {
+window.onbeforeunload = function() {
     disconnect();
-});
+};
 
 //websocket connection
 function connect(target) {